Chapter 5: Thin-Film Transistor Flat Panel Array Image Acquisition

Is a two-step process: x-ray photons are converted to light, and then the light photons are converted into an electrical signal

Indirect conversion

Material that rapidly absorbs x-rays and produces light:

Thallium-doped cesium iodide (CsI[TI])

The materials used for detecting the x-ray signal and the sensors for recognizing that signal are permanently enclosed inside a rigid protective housing called a:

Flat panel detector

Type of scintillator that is made by growing very thin crystalline needles perpendicular to the detector surface.

Cesium Iodide

Materials that absorb x-rays, resulting in an electrical charge.

Photoconductors

Phosphors that produce light when absorbing x-rays.

Scintillators

The first of these flat panel amorphous silicon and amorphous selenium (a-Se) detectors were introduced in 1995.

Thin-film transistors

Detecting material made of small crystals bound together in an unstructured or turbid layer along with polyurethane material.

Gadolinium Oxysulfide

A type of photodetector that converts light into an electrical charge.

Hydrogenated amorphous silicon

Type of conversion in which x-ray photons are absorbed by the coating material and immediately converted into an electrical signal.

Direct conversion

Consists of a flat panel array with an x-ray absorption material.

Active Matrix Flat Panel Imager

Isolates each pixel element and reacts like a switch to send the electrical charges to the image processor.

Field effect transistor (FET)

Photoconductors are materials that:

absorb x-rays and produce electrical charges

Scintillators are phosphors that:

produce light when absorbing x-rays.

A device that includes a photosensitive array and small pixels that convert light into electrical charges is known as a ______ transistor.

thin-film

A device that acts like a switch to send electrical charges to the image processor in a direct conversion flat-panel detector is known as a ______ transistor.

field-effect

In a flat-panel detector, specialized silicon integrated circuits control

line scanning sequence

Flat-panel detectors that use indirect conversion technology convert

x-rays to visible light.

Indirect conversion in flat-panel detectors is a ____-step process.

two

The type of flat-panel detector that uses thin films of silicon integrated with arrays of photodiodes is known as a(n):

amorphous silicon detector

A Gd2O2S scintillator is known as what type of phosphor?

both turbid and unstructured

Manufacturers make efforts to maintain a standard of less than ________ defective pixels.

0.1-0.2%

True or False: The absorption material can be attached to the pixel array electrically or physically.

True

True or False: The 2-D array determines whether the imager is direct conversion or indirect conversion.

False

True or False: Gain calibration will remove inherent detector artifacts from an image.

True

True or False: Offset correction is used to remove inherent signal that remains in a detector.

True

True or False: All flat-panel detector systems have the ability to take images faster than the detector can accommodate.

False

True or False: Because of how the CsI crystals are grown, they are considered a structured scintillator.

True

True or False: There is a possibility in any imaging system of losing or misrepresenting image information because of defects in the operation components of the device.

True

True or False: There are two ways to measure detector performance: numerical measurement of spatial resolution and SNR.

False

True or False: In direct conversion, x-ray photons are absorbed by the scintillator and immediately converted into an electrical signal.

False

True or False: If an image is taken prior to the detector releasing all of the signal from the previous image, a faint image of the previous exposure may be visible. This is known as image lag.

True

True or False: Offset correction determines the amount of signal inherent in the detector.

True

True or False: Structured layers produce more scattered light than unstructured layers, thereby decreasing the efficiency of the detector.

False

True or False: A phosphor scintillator requires a photodiode or phototransistor to detect light.

True

True or False: Gadolinium oxysulfide (Gd2O2S) detecting material is made from small crystals bound together in an unstructured or turbid layer along with a polyurethane material.

True

True or False: manufacturers make efforts to maintain a standard of less then approximately 1% to 2% defective pixels and build software programs into their systems to identify and isolate dead pixels.

False

True or False: When the exposure is made, the sensing/storage component within the pixel contains the image information.

True